Ceiling panels, particularly acoustical ceiling panels, are often made from a loose mass of slightly compacted mineral wool fibers. The low density characteristics of these panels are needed to obtain desirable acoustical qualities. Yet the nature of mineral wool is such that it loses strength and deforms when exposed to temperatures beginning at about 700.degree. C. such as are encountered when a fire breaks out in a room containing mineral wool acoustical ceiling panels. Deformation of the entire panel occurs when the individual mineral wool fibers shrink under viscous flow and allow the panel to fall from the ceiling. This dropping of the ceiling panels during a fire exposes the plenum and the under surface of the structure above the room to the fire conditions. Thus, the spread of the fire is enhanced.
Accordingly, it is desirable to make a panel of mineral wool fibers which preserves the needed acoustical properties and yet which sufficiently withstands predictable fire conditions to delay the fall of the panel from the ceiling and thus to retard the early spread of the fire. At the same time, the acoustical ceiling panel must withstand the normal ambient conditions to which all acoustical ceiling panels are exposed during use. Any treatment of the mineral wool fibers must be such that when exposed to the normal moisture and air in a room, the treating system does not stain the ceiling, become too acid or too basic and thus destroy the fibers, and not release any objectionable odors during the normal life of the panel, or release noxious gases during the fire. It is the primary object of the present invention to present a panel which meets these requirements.